Phantom powered buffer in a cable?

[ACS]

I've been scouring google and searching here for a design for a buffer that a) can be phantom powered (ie 48v) and b) is simple enough to build into a cable itself. No luck in my searching - anyone have any ideas?

Basically, my home studio has a little Behringer mixer as the front end - but of course I need to run through a buffer to be able to plug my guitar into this due to the low input impedance. I don't have the luxury of being able to leave this set up (due to limited space) so I'm getting sick of having to pull out pedals, extra cables, wall wart etc just. To plug my guitar in for a few minutes. I figure that if I just have one cable that I can plug in directly, then i can far more quickly record quick sketches - before the inspiration goes!

Any thoughts?

[amptramp]

I have an alternative suggestion: use a process control circuit.  These provide a 4 to 20 mA current loop where the current flow in the circuit would be set by circuitry at the guitar end of the cable and the corresponding box on the other end provides a supply (such as 9 volts, but possibly any larger value as well) and a 100 ohm resistor to ground.  The output is 0.4 to 2.0 volts across the resistor.  The amplifier at the guitar end of the cable takes in the voltage and uses an op amp (obviously, one with less than 4 mA quiescent current) and provides a current output that is proportional to voltage input - a transconductance stage.  These are uised extensively in process control applications in factories where they want to avoid problems from ambient noise.  The zero input would produce a 12 mA output and would vary by ±8 mA.

The circuit is simple if you use the guitar end circuitry as a current sink and use a differential amplifier across the 100 ohm resistor.  Process control circuitry is used in a high-noise environment such as welding robots, chemical control in the presence of pump switching noise etc.  It requires two wires and they can be coaxial audio cable.  It should be much better than phantom power which requires more wires.

[tempus]

http://www.till.com/articles/GuitarPreamp/

http://www.till.com/articles/PreampCable/index.html

http://www.hawestv.com/amp_projects/fet_preamp/fetpreamp1.htm

[ACS]

http://www.till.com/articles/GuitarPreamp/

http://www.till.com/articles/PreampCable/index.html

http://www.hawestv.com/amp_projects/fet_preamp/fetpreamp1.htm

Nice, that looks to be getting close. Both circuits are designed for 9V - I'm not clever enough to figure out whiter they'd run at 48v as they stand, or whether significant mods (or some serious voltage regulation) would be required. Any thoughts?

[Processaurus]

http://www.jensen-transformers.com/as/as004.pdf

Boom.

A great circuit from Jenson's app notes, I've used it as a DI input for a studio quality mic preamp.

[tempus]

The 2nd Tillman article states:

"As an extra feature, it turns out that the Preamp Cable can just as well be used with standard phantom powered microphone inputs on a mixer (48 Volt, 6.8 Kohm, balanced).  This is the way I typically use it."